[rrd-users] RRD Database precision

Sam Stickland sam_mailinglists at spacething.org
Thu Aug 14 12:58:17 CEST 2008


I did some testing on my perl build (v5.8.8 built for 
i386-linux-thread-multi, RHEL 5.2), and found that it can support up to 
15 digital of precision at e99, which trumps rrdtools's XML export by a 
factor of 1e4.


Sam Stickland wrote:
> Hi,
> I'm optmising a perl RRD replay script I've written (it "replays" DSs 
> from one RRD to another, preserving max and average information as best 
> possible, even when the RRA definitions are notably different). At the 
> moment, I've got somewhat liberal use of Math::BigFloat, and I envisage 
> quite a notable speed increase if I use the native floating points where 
> possible.
> What precision does RRD store it's information in? Looking at the output 
> of "rrdtool dump" I see 11 decimal digits and an exponent, so this 
> should be storable within perl's native float, with a bit of precision 
> left over (room for an extra five decimal places)? 
> (http://perldoc.perl.org/perlnumber.html).
> So I should be able to work with perl's native floats, and only invoke 
> Math::BigFloat when I need to round it to a native integer for passing 
> to RRD?
> Is this right?
> Sam
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